1. Field of the Invention
The present invention relates to a battery safety device adapted to form an electrical circuit and convert a charged state of the battery to a discharged state when compressed by a predetermined pressure or higher. Also, the present invention relates to a battery having the safety device.
2. Description of the Related Art
As recent electronic appliances rapidly become wireless and portable, a non-aqueous electrolyte secondary battery having large capacity and high energy density has been developed as their driving power source. However, such a non-aqueous electrolyte secondary battery is exposed to danger in that, when a strong external pressure or an external impact caused by a nail or nipper is applied, the interior of the cell is damaged and the cell may ignite or explode.
In particular, since the positive electrode active material is sensitive to voltage, the reactivity between the positive electrode and the electrolyte increases as the battery is charged and the voltage rises. The surface of the positive electrode then decomposes and oxidation reaction occurs to the electrolyte. This increases the danger of fire or explosion.
Such a safety problem becomes more important as the battery, specifically the non-aqueous electrolyte secondary battery (for example, lithium secondary battery), has larger capacity and higher energy density.